Annular heat exchanger

ABSTRACT

An annular heat exchanger comprising at least two circumferentially enclosed tube profiles ( 1, 2 ) arranged inside each other for media flow and having a thermal conductive structure ( 3 ) arranged inside. The thermal conductive structure ( 3 ) comprises a helically tightly wound pair of bands ( 4, 5 ) lying on each other, the first band ( 4 ) being smooth, the other band ( 5 ) being corrugated transversally to the winding direction to create flow channels ( 6 ).

TECHNICAL FIELD

The invention relates to an annular heat exchanger comprising at least two circumferentially enclosed tube profiles arranged inside each other for media flow and having a thermal conductive structure arranged inside.

PRIOR ART

Heat exchangers comprised of at least two tubes for media flow arranged inside each other are sometimes referred to as “tube-in-tube” exchangers. The tube in “tube-in-tube” exchangers has two principal functions—it separates the media and at the same time serves as a heat-exchange surface. Thermal convection from the media to the heat exchanger material is decisive for the exchange of heat, while thermal conduction is present to a minimal extent, just by the tube wall.

Increasing the heat exchange surface increases the output of the heat exchanger. In the “tube-in-tube” exchanger the tube length needs to be increased to increase the heat-exchange surface. As the tube separates the media at the same time, the entire heat exchange surface must have such a wall thickness to withstand the pressures of the media and their pressure difference. This makes the weight and size of such exchangers very large.

The heat exchange surface can be increased by finning. The fins are part of the tube and have a thickness on the order of mm. In this case, both thermal convection and thermal conduction are partly present, but thermal convection is still decisive.

Finning (increasing of the heat exchange surface) is used unilaterally—inside or outside.

To achieve maximum output with a minimum exchanger weight, there is an effort to reduce the thickness of the wall separating the media, which is restricted by technological limits especially if media having high or different pressures are concerned. In addition, these thin walls need to be joined in a way—e.g. by soldering or welding in the case of plate exchangers. This has certain technological limits as well.

A tube for exchangers, filled with a heat-exchange surface having the shape of fins is known from the patent U.S. Pat. No. 6,533,030.

Further, heat exchangers are known that are filled with a honeycomb-shaped structure. The Japanese patents JPH02150691 and JPS62288495 can be mentioned as an example.

Further, rotary regenerative heat exchangers made e.g. by the company KASST are known, which use the condenser principle, which means that they are cyclically charged and after the charged part of the heat exchange surface is turned to a place with a lower temperature they are discharged again. This is quite a different functional principle from that of “tube-in-tube” exchangers from the technical point of view.

The object of the invention is to adapt known “tube-in-tube” exchangers to achieve a considerable weight reduction and an increase of the exchanger output.

DISCLOSURE OF INVENTION

The said object is achieved through an annular heat exchanger comprising at least two circumferentially enclosed tube profiles arranged inside each other for media flow and having a thermal conductive structure arranged inside according to the invention, the principle of which is that the thermal conductive structure comprises a helically tightly wound pair of bands lying on each other, the first band being smooth, the other band being corrugated transversally to the winding direction to create flow channels.

An advantage of the invention is that the individual thermal conductive structures are separated from each other by the respective tube profiles which work as a heat exchange surface in standard exchangers, but in the inventive exchanger they predominantly act as media separators. The tube profiles do not primarily form a heat exchange surface, but a piece of the exchanger that separates the media so the tube profiles can be sized to the respective pressure difference and the exchanger according to the invention can be used for almost any media pressure difference. Since the thermal conductive structure can have a thickness of tens of micrometers regardless of the media pressures while the thickness of the wall and possible fins in finned tubes of known exchangers is on the orders of millimeters, i.e. 2 orders thicker, the weight of the exchanger according to the invention is considerably lower at the same output.

The tube profiles can have in principle any cross-section, especially circular, oval, or rectangular.

The thermal conductive structure preferably fills the tube profiles completely.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows a cross-section of the first example of an annular heat exchanger according to the invention.

FIG. 2 shows a detail of the design of the thermal conductive structure in the area of the inner profile.

FIGS. 3, 4, 5 and 6 show other embodiments of annular heat exchanger according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of an annular heat exchanger according to FIG. 1 comprises three concentrically arranged tube profiles for media flow, namely the outer profile 1, inner profile 2 and central profile 7. In this embodiment, the tube profiles 1, 2, 7 consist of tubes with a circular cross-section The intermediate spaces between these profiles 1, 2, 7 are completely filled with a thermal conductive structure 3 that is composed of a helically tightly wound pair of bands 4, 5 of aluminum sheet with the thickness of 0.05 mm, lying on each other. The first band 4 is smooth while the other band 5 is corrugated transversally to the winding direction to produce flow channels 6 (see FIG. 2).

The embodiment of an annular heat exchanger according to FIG. 3 only differs from the embodiment of FIG. 1 in that it does not have a central profile 7 and that the entire inner profile 2 is completely filled by the thermal conductive structure 3.

The embodiment of an annular heat exchanger in accordance to FIG. 4 comprises several central profiles 7. In such a case, there may be two media, or the exchanger can be designed for heat exchange between more media.

FIGS. 5 and 6 show examples of exchangers whose tube profiles 1, 2 have a rectangular cross-section. A skilled person will find it obvious that the profiles 1, 2, 7 can virtually have any cross-section with enclosed circumference.

The annular heat exchanger according to the present invention can be connected as a counter-current or co-current exchanger with any number of inserted profiles 1, 2, 7. The exchanger can also be used for liquid/liquid media, but its benefits are maximally manifested when used for gas/gas and gas/liquid media and in applications with a high pressure difference at the hot and cold side (steam generators, recuperators of combustion turbines, condensers, evaporators).

The function of an annular heat exchanger according to the present invention will be described using the embodiment shown in FIGS. 1 and 2. The other embodiments work in an analogous way.

Hot medium is supplied to the space between the inner profile 2 and the central profile 7 where the medium transfers heat by convection into the thermal conductive structure 3. The thermal conductive structure 3 conducts this heat to the tube that forms the inner profile 2 and subsequently the heat is conducted to the thermal conductive structure 3 that fills the space between the inner profile 2 and the outer profile 1. In this space, the thermal conductive structure 3 transfers heat by convection into the colder medium that flows in this space. The motion of heat is indicated with arrows in FIG. 2.

Thus, the annular heat exchanger according to the present invention is based on combined heat exchange when thermal convection has the same importance as thermal conduction. Its heat transfer surface is maximized by insertion of the thermal conductive structure 3 described above. Heat transfer into this thermal conductive structure 3 and the subsequent thermal conduction by this thermal conductive structure 3 to the separating wall of the respective profile 1, 2, 7 are equally used for the heat exchange. Thus, thermal conduction by the thermal conductive structure 3 is applied to a considerably higher extent, being equally important as thermal convection in the exchanger based on the present invention.

Individual thermal conductive structures 3 are separated from each other by the respective tube profiles 1, 2, 7, which work as a heat exchange surface in standard exchangers, but in the inventive exchanger they predominantly act as media separators.

As the media are separated by the tube profiles 1, 2, 7 that are designed for the respective pressure difference, the exchanger based on the present invention can be used for virtually any pressure difference of media. Thus, the tube profiles 1, 2, 7 do not primarily form a heat-exchange surface, but a media-separating part of the exchanger. Since the thermal conductive structure can have a thickness of tens of micrometers regardless of the media pressures while the thickness of the wall and possible fins in finned tubes of known exchangers is on the orders of millimeters, i.e. 2 orders thicker, the weight of the exchanger according to the invention is considerably lower at the same output.

A comparison calculation utilizing a numerical model in the ANSYS CFD program was used to compare the heat output transferred by a 50-mm aluminum tube with the diameter of 20 mm in four versions, simulating 4 different types of exchangers:

-   -   —smooth tube     -   —standard finned tube     -   —finned tube according to the patent U.S. Pat. No. 6,533,030     -   —exchanger in accordance with the invention

Calculation conditions: a tube heated from the outside to the constant temperature of 100° C.; air entering the tube having the temperature of 20° C. and flow speed of 31.87 m/s.

An ideal exchanger having 100% efficiency would have the output of 604 W. Using the numerical model, the following values were calculated:

Smooth tube—32 W (5% of the ideal exchanger)

Standard finned tube—146 W (24% of the ideal exchanger) Finned tube according to the patent U.S. Pat. No. 6,533,030—252 W (42% of the ideal exchanger) Exchanger in accordance with the invention—375 W (62% of the ideal exchanger)

From the above it is obvious that the inventive exchanger has by far the highest output.

LIST OF REFERENCE SIGNS

1 outer profile 2 inner profile 3 thermal conductive structure 4 first band 5 second band 6 flow channel 7 central profile 

1. An annular heat exchanger comprising of at least two circumferentially enclosed tube profiles arranged inside each other for media flow and having a thermal conductive structure arranged inside, wherein the thermal conductive structure comprises a helically tightly wound pair of bands comprising a first band and an other band lying on each other, the first band being smooth, and the other band being corrugated transversally to a winding direction to create flow channels.
 2. The annular heat exchanger according to claim 1, wherein the tube profiles have a circular, oval or rectangular cross-section.
 3. The annular heat exchanger according to claim 1, wherein the thermal conductive structure completely fills the tube profiles.
 4. The annular heat exchanger according to claim 2, wherein the thermal conductive structure completely fills the tube profiles. 